Stress in cats with rapid mouth opening and breathing is usually caused by a new environment, strangers, being frightened, changing food, or other stimulation. You need to take the cat to a quiet place and let the cat relieve itself. If If the cat cannot relieve itself, it is best to send it to a pet hospital for examination and treatment to avoid life-threatening injuries.
Tips:
Generally, heat stroke, poisoning, abnormal heart function, respiratory infection, etc. can also cause cats to have shortness of breath. So you need to pay more attention.